Free androgen index (FAI)

FAI provides a more accurate assessment of androgen status than total testosterone alone, especially when SHBG levels are abnormal. In women, elevated FAI can indicate polycystic ovary syndrome (PCOS), helping explain symptoms like irregular periods, hirsutism, acne, and fertility issues. In men, low FAI may reveal functional testosterone deficiency even when total levels appear normal, particularly in obesity, aging, or metabolic syndrome where SHBG changes mask true hormone availability. The index is especially valuable for detecting subtle hormonal imbalances that contribute to sexual dysfunction, mood changes, muscle loss, or metabolic problems, guiding more targeted hormone optimization strategies.

At baseline / for screening: Once every 12 months from age 30 as part of a hormone panel, drawn in the morning between 7 and 10 AM when testosterone peaks.

When monitoring an intervention or change: Retest 6 to 12 weeks after starting or adjusting testosterone replacement therapy (gel, injection, pellet) to confirm you've reached the target range. Once stable on a dose, retest every 6 to 12 months. After meaningful body composition changes (weight loss, training, sleep improvement), expect 3 to 6 months for natural testosterone to shift.